1. Field of the Invention
The present invention relates generally to the field of artificial mechanical heart valves (MHV), and in particular to a tri-leaflet MHV with a smooth and streamlined curved surface that effectively prevents clotting and hemolysis while forming a sturdy and firm seal when closed.
2. Description of Prior Technology
Heart valve replacement surgery is one of the most mature and effective therapies for valvular diseases. This type of operation has become a regular surgical procedure since the commercialization of the first artificial heart valve in 1966. Clinically, the postoperative death rate is below 5%. On average, successful heart valve implantation may extend patient life for more than 10 years. Currently, the demand for artificial heart valve replacement surgery is approximately 200,000 patients each year.
Generally, there are two major types of artificial heart valves. The first type is the Mechanical Heart Valve (MHV), which is completely composed of artificial materials. The second type is the Bioprosthetic Heart Valve (BHV), which consists of chemically treated biomaterials. Pyrolytic carbon (PyC) has become the most commonly used material for MHV since it was first introduced for clinical implantation in 1969. Single leaflet and bi-leaflet MHVs made of PyC became common in the late 1970's and have since been used in the treatment of valvular diseases. Up to now, more than two million PyC heart valves have been implanted in human bodies and the accumulated clinical experience exceeds two hundred thousand patient-years.
BHVs are chemically treated animal valves, such as pig and ox. Their geometry is similar to the human valve and is thus commonly used by medical doctors. However, the BHV suffers from calcification and tissue regression, making it unsuitable for patients aged below 30.
Although MHV does not exhibit calcification and tissue regression, clinical reports indicate MHV often causes thrombosis and thromboembolism. The MHV patients must continuously take anticoagulants for life in order to reduce the risks of these complications. This has been one of the biggest problems with MHV implantation. The intake of anticoagulants may increase the incidence of hemorrhagic diseases and threaten the life of MHV patients. Moreover, long term medication may cause cardiac complications like endocarditis, hemolysis and so on. Although the incidence of cardiac complications is low, it cannot be neglected.
MHV basically contains one or more leaflets, an annular valve base, a hinge and a sewing ring. The leaflets are occluders for the opening and closing of the valve, which operates 0-200 times every minute inside the human body. The valve base serves as a frame for holding the occluders. The hinge rotatably supports the leaflets in the valve base. The sewing ring is a woven material surrounding the MHV for attachment to the implantation site. The leaflets, the annular valve base and the hinge still need improvements from the viewpoint of fluid dynamics.
Bi-leaflet heart valves form three streams when the two leaflets are opened, which is non-symmetric with respect to a center of the heart valve. Non-hermetic compliance with the aortic sinuses leads to non-symmetric flow profile, thus inducing a large velocity gradient and turbulence. Since the bi-leaflet MHV is centrally asymmetric, the two leaflets are not opened synchronously, leading to great recirculation of blood and increasing the burden of heart. To overcome such deficiencies, new tri-leaflet heart valves are continuously designed.
Hemodynamically, the tri-leaflet heart valve opens to form a single central flow, similar to the operation of the human aortic valve. The pressure induced by the circulation of blood inside semi-circular aortic sinuses downstream the heart valve helps to open and close the heart valve. The most important factors in the design of the tri-leaflet heart valve are the shape of the leaflets and the pivoting mechanism.
Conventional tri-leaflet heart valve designs use protruding supports to control the opening of leaflets. For example, U.S. Pat. No. 5,843,183 discloses a support member that extends from the annular valve base to support the corresponding leaflet. Leaflet movement from open to closed position is controlled both by upstream retainers aligned with the flat central sections of each leaflet and by surfaces on the side walls of the projections along which the leaflets slide. In U.S. Pat. No. 6,395,024, two support members support each corresponding leaflet. The disadvantage associated with these prior designs is that the support member and the leaflet will create wakes and turbulence of the blood flow.
Other examples of conventional tri-leaflet heart valves are disclosed in U.S. Pat. Nos. 4,446,577 and 5,522,886, wherein a pair of projections on the sides of the leaflet fit into slots inside the annular valve base and pivotally support the leaflet. In U.S. Pat. No. 5,628,791, a boss slides and rotates inside the slot to control the leaflet The complicated manufacturing process and occurrence of thrombosis are the main disadvantages.